In recent years, RFID systems for recognizing and managing people and goods in an automatic manner are becoming widespread rapidly.
An electromagnetic field emitted from an antenna used for RFID systems has three fields, i.e., a quasi electrostatic field, an induction field, and a radiation field, and the strengths of these fields are in inverse proportion to the cube of the distance from the antenna, the square of the distance from the antenna, and the first power of the distance from the antenna, respectively.
When the communication methods of RFID systems are classified from this point of view, they will be divided roughly into an induction field coupling system using an induction field in LF band or HF band, and a radiation field coupling system using a radiation field in UHF band.
As for the former one, i.e., the induction field coupling system, RFID systems making use of a band of 125 kHz through 135 kHz of the LF band are used in the FA (Factory Automation) field of factories, etc., around from the 1980s. In addition, RFID systems using a 13.56 MHz band of the HF band are widely used for security management for entering or leaving a room, security management of entrance and exit, fare payment in public transportation facilities such as buses, railroads, etc.
On the other hand, the latter one, i.e., the radiation field coupling system, uses frequencies of 433 MHz band, 860 MHz to 960 MHz band, and 2.45 GHz band, has a long communication range as compared with the former, and is mainly being put into practical use for purposes such as physical distribution management, parts management in production plants, etc.
However, at present, the former induction field coupling system, in particular an HF band RFID system, is most widely prevalent.
In such a situation, there is a demand that users want to hold an existing HF band RFID system as it is, and in addition thereto, to newly introduce a UHF band RFID system. In this case, considering users' convenience, it is not desirable that the users each own a plurality of tags for use with the individual RFID systems, respectively, but it is instead desirable that the users can cope with the plurality of RFID systems by the use of only one tag.
From such a background, in recent years, there have been made the research and development of the card-type RFID tags which are available on both of the HF band RFID system and the UHF band RFID system. As an example, there has been proposed a method of forming a UHF band communication dipole antenna at the inner side of an HF band communication coil conductor which is formed on a card (for example, see a first patent document and a first nonpatent document).
That is, as a method of arranging the HF band communication coil and the UHF band communication antenna in one sheet of card, there are roughly two methods of arrangements, i.e., one method of arranging a UHF band antenna at the inner side of an HF band coil as described in the first patent document and the first nonpatent document, and the other method which is different from this and in which a UHF band antenna is arranged at the outer side of an HF band coil.
[Prior Art References]
[Patent Documents]
[First Patent Document] Japanese patent application laid-open No. 2004-240899
[Nonpatent Documents]
[First Nonpatent Document]
K. S. Leong, M. L. Ng, and P. H. Cole, “Miniaturization of dual frequency RFID antenna with high frequency ratio” 2007 IEEE Antennas and Propagation Society International Symposium Digest, pp. 5475-5478, July 2007